The present invention relates to transformers and more particularly to dry type transformers with improved cooling features.
As is well known, a transformer converts electricity at one voltage to electricity at another voltage, either of higher or lower value. A transformer achieves this voltage conversion using a primary coil and a secondary coil, each of which are wound on a ferromagnetic core and comprise a number of turns of an electrical conductor. The primary coil is connected to a source of voltage and the secondary coil is connected to a load. The ratio of turns in the primary coil to the turns in the secondary coil (“turns ratio”) is the same as the ratio of the voltage of the source to the voltage of the load.
A transformer may be cooled by air or a liquid dielectric. An air-cooled transformer is typically referred to as a dry-type transformer. In many applications, such as in or around commercial buildings, it is preferable to use a dry-type transformer instead of a liquid-cooled transformer. Often, the coils of a dry-type transformer are coated with, or cast in, a dielectric resin using vacuum chambers, gelling ovens etc. Encapsulating a coil in a dielectric resin protects the coil, but creates heat dissipation issues. To dissipate the heat from around the coil, cooling ducts are often formed at predetermined positions within the coil. Such cooling ducts improve the operating efficiency of the coil and extend the operational life of the coil. An example of a resin-encapsulated coil with cooling ducts is disclosed in U.S. Pat. No. 7,023,312 to Lanoue et al., which is assigned to the assignee of the present invention and is hereby incorporated by reference.
Although the use of cooling ducts produces good results, the creation of cooling ducts in a coil increases the labor and material costs of the coil. Accordingly, it would be desirable to provide a transformer with resin-encapsulated coils that reduces or eliminates the use of cooling ducts. The present invention is directed to such a transformer.